This invention relates generally to suspension systems of wheeled vehicles. More particularly, the invention relates to suspension system controls, specifically to a lift axle control for controlling the raising and lowering of a lift axle in a wheeled motor vehicle, such as highway tractor having an auxiliary lift axle that can be selectively raised and lowered, to selectively disengage its wheels from and engage its wheels with, the underlying road surface or terrain.
A lift axle suspension system allows a lift axle to be selectively raised and lowered with respect to the undercarriage of a vehicle. When the lift axle is lowered, its wheels engage the underlying road surface or terrain, enabling the lift axle to bear some portion of the vehicle weight, while relieving some of the vehicle weight borne by other wheels that are engaging the underlying surface. When the lift axle is raised, its wheels disengage the underlying surface so that the lift axle ceases to support a portion of the vehicle weight.
The chassis of a heavy truck, a dump truck for example, typically has a pair of front wheels for steering the vehicle and a rear axle having driven wheels coupled through a differential to a driveshaft that extends from an output shaft of the transmission. Such a vehicle may also have an auxiliary lift axle in tandem with the driven rear axle.
When such a vehicle is hauling a load, the auxiliary axle may be lowered to bear some of the weight imposed on the vehicle by the impending load. When the vehicle is not loaded, the added support provided by the auxiliary axle may be unnecessary, in which event the auxiliary axle may be raised to disengage its wheels from the underlying surface. This can provide certain benefits that include a reduction in engine torque load allowing the vehicle to travel with better fuel economy, better vehicle maneuverability, and avoidance of wear on the auxiliary axle and its wheels and tires.
The suspension of a lift axle in a vehicle comprises load air springs disposed between the lift axle and the vehicle frame proximate the wheels at opposite ends of the lift axle. Inflating the load air springs lowers the lift axle to place its wheels on the underlying surface in support of the vehicle. The inflated load air springs may serve as at least a portion of the suspension of the lift axle from the vehicle undercarriage.
Lift air springs are disposed proximate the ends of the lift axle, in association with the suspension. Inflating the lift air springs, while deflating the load air springs, raises the lift axle to disengage its wheels from the underlying surface.
A known auxiliary lift axle control operates in a manner that causes a raised lift axle to be lowered when a vehicle on-off switch, sometimes called an ignition switch, that has been turned off to stop the vehicle engine, is once again turned on. The lowered lift axle can then be raised by the driver""s operation of a switch. The known control also causes a lowered lift axle to be raised whenever the vehicle transmission is placed in reverse gear. Raising a lift axle when the vehicle is being driven in reverse may avoid the potential for damaging certain components of a lift axle, such as steering components of a steerable lift axle.
The present invention arises out of a belief that a preferred mode of operation for lowering a lift axle in some vehicles, like the one just described for example, should require an intentional act on the part of the vehicle driver that is additional, and subsequent, to the act of turning the ignition switch from off to on. The present invention comprises a control that requires such an additional intentional act by the driver in order to lower the lift axle. Yet, the disclosed preferred embodiment of the inventive control retains the automatic lifting of a lowered axle whenever the vehicle transmission is placed in reverse or whenever the ignition switch is turned off.
The preferred embodiment is constructed from known electric circuit devices connected to form a novel control circuit for a lift axle control. The devices include a momentary ENABLE switch, a latching relay, a REVERSE GEAR relay, and a two-position RAISE-LOWER selector switch for the lift axle. The novel control circuit is also coupled with the vehicle electrical system to receive both electric power and a REVERSE GEAR signal from the vehicle system.
The invention provides a cost-efficient solution for accomplishing the desired control functions for a lift axle.
One general aspect of the invention relates to a wheeled motor vehicle comprising an ignition switch for turning the motor of the vehicle on and off and an auxiliary lift axle that can be raised to lift wheels of the lift axle off an underlying surface on which the vehicle is supported and that can be lowered to place the wheels of the lift axle on the underlying surface. A control for raising and lowering the lift axle comprises a circuit that is fed through the ignition switch when the ignition switch is on but not when the ignition switch is off and that comprises a first switch device that requires actuation to enable the lift axle to be lowered and a second switch device that, once the first switch device has been actuated to enable the lift axle to be lowered, is effective upon being actuated to cause the lift axle to be lowered.
Another general aspect of the invention relates to a control for raising and lowering a lift axle on a motor vehicle having any ignition switch for turning the motor on and off. The control comprises a circuit that is fed through the ignition switch when the ignition switch is on but not when the ignition switch is off and that comprises a first switch device that requires actuation to enable the lift axle to be lowered and a second switch device that, once the first switch device has been actuated to enable the lift axle to be lowered, is effective upon being actuated to cause the lift axle to be lowered.
The foregoing, along with further aspects, features, and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. The disclosure includes drawings, briefly described as follows.